Presentation on theme: "Weathering, Erosion, & Deposition"— Presentation transcript:
1Weathering, Erosion, & Deposition The surface features of the Earth change as a result of observable physical and chemical processes
2Weathering and Erosion This is a monument called Cleopatra’s Needle. It was carved in Egypt around 1450B.C. The sides are carved with hieroglyphs, the writing of ancient Egypt. It stood in the dry, hot Egyptian desert for over 3000 years. During that time, the hieroglyphs remained distinct.
3WeatheringIn 1800, the monument was moved to New York City. Almost immediately, the hieroglyphs began to fade. In only a few years in the wet and variable climate of New York, the Egyptian writing became indistinct!
4ErosionCleopatra’s Needle was carved from granite, a hard tough, crystalline rock.Although it is tough, granite is changed by the atmosphere.Some of the minerals that make up granite change to clay.Chips and flakes of minerals break away from the granite surface.
5The Cycle of Changing Earth’s Surface Weathering, erosion, and deposition act together in a cycle that wears down and builds up Earth’s surfaceWeathering-wears down the Earth’s surfaceErosion-moves the Earth’s surface (acts as a bridge between the weathering and deposition)Deposition-builds up the earth’s surface
7WeatheringThe breaking down and/or wearing away of earth materials (rocks) into smaller piecesMust occur before erosion can happenNo movement is involved
8Physical aka Mechanical Weathering Breaks rocks down into smaller pieces (nothing changes but the size)Sediments: naturally-occurring material that is broken down by processes of weathering; small/tiny pieces of rockSediments vary in sizes and are named depending on their size
9Weathering Physical Common weathering processes: Frost action Thermal Expansion and Contraction(wetting and drying)Biological ActivityExfoliationAbrasion
11Types of Mechanical Weathering Thermal Expansion & Contraction (Wetting & Drying)Especially effective at breaking up rocks that contain clay.Clays swell up when wet and shrink when dry.Causes rocks that contain clay, such as shale, to fall apart.
13Types of Mechanical Weathering Frost action or Ice Wedging:Water takes up about 10% more space when it freezes.Expansion puts great pressure on the walls of a container.Water in the cracks of rocks wedges the rock apart when it freezes.Often occurs in places where temperatures vary from below and above the freezing point of water.
15These mountains in Salt Lake City were weathered by abrasion. Abrasion is the grinding action of other rock particles due to gravity or the motion of water, ice or air.Most often seen in running water, the beach, or the desert
17Types of Mechanical Weathering Action of plants and animals (biological activity)Larger trees and shrubs may grow in the cracks of boulders.Ants, earthworms, rabbits, woodchucks, and other animals dig holes in the soil.These holes allow air and water to reach the bedrock and weather it.
18Types of Mechanical Weathering Granite exfoliation
19ExfoliationOccurs when thin layers of rocks break off in sheets
20Chemical WeatheringOccurs when chemical reactions dissolve or change the minerals in rocks (rusting, acid breakdown, etc)Occurs most often in warm and humid climatesThis cave was formed by slightly acidic water dissolving the limestone
21Chemical Weathering Breaks down rock through chemical changes. The agents of chemical weatheringWater: dissolves rock over timeOxygen: combines with iron to form rust (oxidation)Carbon Dioxide: dissolves in water to form carbonic acidLiving Organisms: plant roots secrete acidsAcid Rain: from the burning of fossil fuels
23Living OrganismsLichens that grow on rocks produce weak acids that chemically weather rock.
24OxygenIron combines with oxygen in the presence of water in a processes called oxidation.The product of oxidation is rust.
25Carbon Dioxide Dissolves easily in water. Forms a weak acid called carbonic acidThe same compound that is in carbonated drinks.Carbonic acid easily weathers limestone and marble.
26Acid RainCompounds from burning coal, oil and gas react chemically with water, forming acids.Carbon dioxide and sulfur compounds released by industries unite with water in the atmosphere to form acid rain.Increasing amounts of acid rain in the environment increase the rate of chemical weathering.Acid rain causes very rapid chemical weathering.
28Physical and Chemical Weathering Rate of weathering depends on:Climate—warm and humid is fasterSize of the rock particleMineral composition—determines how fast a rock weathersTime—most important factorGiven enough time all rocks with weatherRock Type—rock that is permeable (has holes that let water in), weathers faster than rock that is impermeable.Weathering creates either sediment or soilClassified by size—sand, silt, or clay
29Check for KnowledgeHow does the size of the rock particle affect weathering?How does the mineral composition of the rock particle affect weathering?Why is time the most important factor?
30Lets comparePlease draw a Venn diagram and compare chemical and physical weathering.How are they similar/different?
31ErosionThe movement of weathered earth materials by moving water, wind, gravity or iceEx: waves causing beach erosion (shoreline of Texas is disappearing) running waterEx: sand storm windEx: rain causing a mudslide running water and gravityEx: landslide gravityEx: rain carrying soil and gravel down a driveway running water and gravity
32What are the 4 main ways water erodes? RunoffStream ErosionWave ActionGlaciers
33ErosionThe Bernard Glacier in Alaska's Saint Elias Mountains looks like a huge alpine highway. Glaciers are slow but highly effective shapers of the land, essentially carrying away anything in their path—from soil and rocks to hills and even the sides of mountains
34Why are glaciers called dirty snowballs? What is glacial till? Glaciers are called dirty snowballs because as they move across the land they carve up the earth’s surface collecting rocks and sediments with the snow.Glacial till is the jagged uneven particles the glacier deposits as it retreats (melts)
35Mass Wasting and Creep Mass wasting—downhill movement by gravity Potential increases with slopeCauses rock slides, slump, mud slides, or avalanches
36Landslides Landslides- A geological phenomenon Includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments.
37SlumpA steep hillside shows a spoon-shaped depression in which material has begun to slide downhill.Occurs along a distinct fracture zone, often within materials like clay that may move rapidly downhill.In some cases the slump is caused by water beneath the slope weakening it.
38Soil Creep Can be almost undetectable. Normally found on weathered mountain slopes.Gravity forces the material to slowly slide downhill, and eventually the signs of creep become evident.Tree trunks curve upward as creep caused them to tilt downhillFence posts and hydro poles may also begin to lean downslope
39Why care about erosion?Human activities such as construction increase the rate of erosion 200, even 2,000 times that amount. When we remove vegetation or other objects that hold soil in place, we expose it to the action of wind/water and increase its chances of erodingThe loss of soil from a construction site results in loss of topsoil, minerals and nutrients, and it causes ugly cuts and gullies in the landscape. Surface runoff and the materials it carries with it clog our culverts, flood channels and streams. Sometimes it destroys wildlife and damages recreational areas such as lakes and reservoirs.
40Bare Slopes vs. Vegetation Stabilized Slopes Mudslide dangerLoss of topsoilClogged storm drainsFlooding problemsExpensive clean upEroded or buried house foundationsSoil in placeLess clean upMinimum erosionProtection for house foundations
41Deposition Ex: sand dune-a deposit of wind blown sand The process of eroded earth materials (sediments) being deposited in a new locationEx: delta-where sediment is deposited where a river flows into an ocean or lake builds up a landformEx: sand dune-a deposit of wind blown sand
42Process of DepositionWhen sediments are released after being transportedUsually when velocity decreasesFactors affecting deposition:Particle size—smaller, the slower the rateShape—more spherical, the faster the rateDensity—more dense, the faster the rate
43Process of Deposition Grade bedding aka Vertical Sorting Velocity of transporting agent reduced quicklySediments of mixed sizesSize of sediment increases with depthHorizontal sortingVelocity decreases slow rate over long distanceLarger first, smaller last—mouth of river
44Erosion and Deposition Meanders are S shaped curves formed by weathering of one bank of a river and deposition of the weathered sediment on the opposite bank of the river.This creates a loop-like bend in a river.
49Notes quiz Deposition is the movement of sediment or rock the settling out of sediment or rockthe breaking down of sediment or rock2) A meander isa) a small river that runs into a larger riverb) a loop-like bend in a riverc) a lake that has been cut off from a river
503) Name 3 methods of erosion control b)c)4) What are riparian buffer zones?